util: make allocation functions abort on OOM

util: make allocation functions abort on OOM

The functions are left returning an "int" to avoid an immediate
big-bang cleanup. They'll simply never return anything other
than 0, except for virInsertN which can still return an error
if the requested insertion index is out of range. Interestingly
in that case, the _QUIET function would none the less report
an error.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>